1. Field of the Invention
The present invention relates to an exposing device for use in a laser printer or the like and, more particularly, to an exposing device for scanning a photosensitive member in a laser printer with a laser beam.
2. Description of Related Art
In the conventional exposing device, a laser beam is generated from a laser beam source according to image information supplied by a control device, and the laser beam is reflected by a polygonal mirror rotated by a mirror motor. The laser beam reflected by the polygonal mirror irradiates a photosensitive drum rotated by a drum motor. Conventionally, three types of exposing devices are known. The first type always rotates the mirror motor, the second type rotates the mirror motor only when the exposing operation is executed, and the third type rotates the mirror motor only when the control device has image information. The third type of exposing device is disclosed in Japanese Pat. laid open SHO 62-84656.
The mirror motor rotates at a high speed and cannot be used for a long time, especially if the mirror motor is always rotated as the first type is. Moreover, since the mirror motor of the first type rotates even when the exposing operation is not being executed, noise is always generated. On the other hand, if the mirror motor of the second type or third type is rotated only when the exposing operation is executed or only when the control device has image information, it is then necessary to delay the exposing operation until the rotational speed of the mirror motor reaches its predetermined rotational speed, when the next exposing operation is started after a prior exposing operation is finished or after prior image information in the control device is completely used. Accordingly, the exposing operation cannot be started immediately.